Present day R. F. power transistor devices contain an uncontrolled, and usually too large, amount of common lead inductance. When transistors are intended for use in the ultra high frequency ranges for example from 400 MHz to two or more gigahertz, the inductance of the leads, usually formed by very small wires extending from the transistor emitter or base to ground, or input, leads and output leads becomes very significant. In such transistor devices, a capacitor which may be of the MOS variety is usually mounted in close association with the transistor chip and one or more of the small wire interconnecting leads extend from the transistor chip to the MOS capacitor and to the input or output leads. The capacitor works in conjunction with the inductance of the various leads in order to provide the desired impedance matching and the like. Inductances in the ranges of nanohenries and even picohenries are values to be reckoned with.
Typical of the prior art is the patent to Litty et al No. 3,713,006 dated Jan. 23, 1973. As shown in Litty, at least in one form of high frequency transistor, the ground conductors are relatively large area leads as are the input and output conductors. The transistor chip has subdivided base and emitter areas from which small wire conductors extend to the appropriate leads. In addition, an MOS capacitor which may have subdivided portions is mounted on the same substrate and small wire leads extend from the subdivided contacts of the capacitor plates to the appropriate other components.
In these prior art high frequency power transistors making the small wire leads as short as possible, placing them in parallel where possible, and having them extend in opposite directions all tend to reduce the common lead inductance. Nevertheless there is, in the prior art devices, always some inductance remaining and usually too large an amount. Moreover it is not easily controllable, if at all.
Also in the prior art transistors, metallized areas are provided on an electrically insulating but thermally conducting layer made, for example, of beryllium oxide and the various components including the ground leads, input leads, output leads, transistor chip and capacitor chip are bonded to the appropriate ones of the metallized areas. The opposite side of the beryllium oxide member is bonded usually to a large metal heat sink while the ground leads in such devices are connected to the appropriate metallization. It is nevertheless difficult to determine where actual ground occurs in the case of the transistors functioning in the high MHz and gigahertz regions. This, of course, further complicates the design problem of determining what actually is the common lead inductance and controlling it.